Solid propellant containing organic oxidizers and polymeric fuel



anneal Patented 77 1954 "ss., assignor, by mesne of America as repretheArmy y 01L A i i957, No. 646,935 3 Claims. (@Cl. 149-19) This inventionrelates to new propellants and more particularly to those propellantsrequiring specified physical thermodynamic ch acteristics such as thosesuitable for small arms ammr on.

The term pro ellant as used herein refers to combustible materials chrequire no further oxygen from the atmospi ch burn rapidly undercontrolled conditions to impart. lnnetic energy to a body.

Present day orcpellants, suitable for small arms ammunition "for exa areprimarily limited to the type :e composition of the propellants to seewith small quantities of other materia s och as nitroglycerin that theperformance of the propellant is confined to a narrow range with respectto llama temperature and impetus (sometimes called force). The simpleexpedient of increasing the nitroglycerin content to raise the flametemperature and impetus of a propellant is not workable becausenitroglycerin exudes or migraes, thus causing the propellant to beunstable and unfit for nded storage.

x 2- present so-cailed 111R propellants (oonslstg roceilulose v 4 smallquantities of ts, etc. re illustrative of the nitrorcpellan'cs now inuse, this standard e propellant \vi'. be used as basis for comparing theimproved characteristic achieved by propellants of this invention.

- by the gun, thermal staities over extended periods and a wide range ofconditions. It is desirable, too

, that a. new type of propella it should give higher for exan e, to thatof lMR) and ual weight or" propellant, s for a lower weight of .r chargeto weight ratios. impetus to we v t ratio ie-ved at burning temt reachedby the present to keep metal erosion nal improvement to .s (about 39cbus an add us for the 'ne or less weight at a lower ver, a new typepropellant cicnt fleidhi ty in composi- "vers or sections. in e ayersving well defined difures, burning rates, etc., the up the ayors must besubstan- 'tend to migrate or his invention to provide J- impetus on anequal and used. it is an lants which have greater 1 1a The tion ratiosof which may be varied to obtain a wide range of such performanceparameters as flame temperature, burning rate, etc. It is still afurther object of this invention to provide propellants which possessgood thermal stability over the accepted military range and which may bestored without any appreciable migration or exudation of the componentmaterials taking place. Yet another object is to provide propellantswhich may be used to make up multi-layer grains. These and other objectswill be seen to be accomplished by the propellants of this inventionwhich are described in detail.

The impetus which is developed by the propellant and imparted to thebullet is a function of the quantity nR'l where n is the number of molesof gas developed from the burning of the propellant, R is the gasconstant expressed in appropriate units, and T is the adiabatic orburning temperature. T he factor n is a function, in turn, of thepropellant composition. T is dependent upon the composition of the finalgas products and the heat of decomposition of the propellant, which inturn may be varied by varying the composition of the propellant.

If T is fixed within a fairly narrow range, for ample at about 390T K.for small arms, it must be m within its limiting composition andstructure of pellant. This composition and structure must be such as togive a specified temperature w same time producing a maximum n, the onlyparameter in the quantity of HRT which may be raised to increase theimpetus of the propellant. if, on the other hand, ,igh flametemperatures are desired for a core-type propellant, for example, thenT, as well as n, can be increased giving a marked increase in the HR?product. In a compound such as nitrocellulose, which generally serves asthe primary component of a small arms propellant, both n and T are, ofnecessity, limited. On the other hand the single compounds which containa iavorable balance of carbon, hydrogen, and oxygen atoms and high heatsof decomposition we generally highly explosive in character. The desiredcharacteristics for a small arms propellant can therefore be morereadily found in a suitable mixture of a high explosive, serving as anoxygen source and a means to increase 12 and T and a fuel providingmaterial to bum. The use of a mixture containing a material with highavailable oxygen content makes possible adjustments in carbon, hydrogenand oxygen ratios, and thus the achieving of desired temperature andimpetus over a wide range.

The fuel may contain oxygen but it is preferably one which is notcapable of sustaining its own combustion without additional oxidants. Inorder to keep the number of components in sit of this invention tominimum, it is desirable that the fuel should also be capable of servingas a binder for the oxidant to make a final propellant which can bereadily handled in such fabricatin equipment as extruders, presses, etc.

I have found that, in accordance with the above discussion, a mixturecomprising a liiglrenergy or anic material as an oxidant; a polymericmaterial, servi g as fuel and binder; and, if necessary, a few percentof suitable ilasticizers or stiffening; and stabilizers, where required,can be so formulated to give a workable, extrudable, and stablepropellant capable of achieving the objects of this invention. l t ispreferable that the oxygen of the organic material be present in suchgroups as a nitrate ester, aromatic nitro, aliphatic nitro, nitramine,azo, azide, nitroso, peroxide, ozonide, perchlorate, etc.

A propellant, for example, made up of the prooer ratios ofbis-(trinitroethyl)-iitramine as the high-energy oxidant, and apolyisobutylenepoiyethylene mixture as the fuel and binder having aburning temperature of about 3080'" K, equivalent to that for lMR, willdevelop an impetus equivalent to some 123% that or" IMR on an cqumweight basis. If it is desired to produce a cool propellant with impetusequal to lit ill, it is possible by increasing the amount of polymer toreduce the adiabatic flame temperature to about 2160" K. To illustratethe improvement of the new type propellant over the present propellantsin yet another manner, it may be shown that an impetus equal to thepresent lMR may be attained by using only about 81% of the newpropellant, density of 1.64 thus decreasing the cartridge volume.

It may be desirable to have propellants which burn at adiabatic flametemperatures considerably higher than 3000 K. to obtain short duration,high velocity firings or for one or more layers of a multilayerpropellant. The compositions described in this invention make such highimpetus, high temperature propellants possible, for by mixing ahigh-oxygen content material with an oxygendeficient fuel binder, it ispossible to adjust the composition ratio to achieve a maximum impetus.This maximum occurs at the point where just enough oxygen is present toburn all the carbon to CO and the hydrogen to H O. For example, in thecase of the bis-(triuitroethyl)-nitr-amine-polyisobutyleire-polyethylenepropellant, the molar ratio at this maximum impetus is 3 to 1 while theweight percents are 95.4% and 4.6% of bis-(-trinitroethyl)- nitrarnineand polyisobutylene-polyethylene, respectively. Impetus developed bythis mixture is equivalent to approximately 150% IMR.

The minimum amount of high-energy oxidant is that which will burn allbut a predetermined amount of all of the carbon present to CO. It is notnecessary to furnish oxygen for burning the hydrogen. The amount ofpermissible free carbon depends upon the application of the propellant,being less Where flash must be kept to a minimum. 7

The maximum amount of high-energy oxidant which can be used depends uponthe burning characteristics desired of the final propellant. That is, itis necessary to limit the quantity of the high-energy ingredient toachieve rapid burning, but not detonation. This means that there shouldnot be more oxygen present than that required toburn all the carbon toCO and the hydrogen to H O. The binding properties of the so-called fuelbinder may also limit the proportions of the constituents. Control ofthe burning properties may also be achieved by adjusting the propellantgeometry and by using suitable deterrents where desired.

In general, the range of the ratio of high-energy material to fuel inthese new type propellants is between the ratios where the final gaseousproducts are CO, H N and Where they are CO H O, N while the better rangeis between the ratios Where the final gaseous products are CO, H O, Nand where they are CO H O, N and the preferred range is between theratios Where the final gaseous products are CO, H N and Where they areCG, H O, N Taking the bis(trinitroethyl)nitramine (G ll; b1 0)-polyisobutylene-polyethylene (C H C H propellant as an example, thegeneral range of the ratio of the former (oxidant) to the latter (fuel)is between 73.5 to 26.5% by weight and 95.4 to 4.6%, while the betterrange is between 87.4 to 12.6% and 95.4 to 4.6%, and the preferred rangein between 73.5 to 26.5 and 87.4 to 12.6%.

The oxidant for this new type propellant is not limited tobis(trinitroethyl)nitramine. Any high-oxygen content, reasonably stablecompound, solid at normal temperatures and pressures, may be used with acompatible polymeric binder. it is preferable, although not necessary,that the oxygen in the oxidant be present in only high-energy groups.Among the other oxidants found to be suitable arecyclotetrarnethylenetetranitramine (HMX) cyclotrimethylenetrinitrarnine(RDX), methylenedinitramine, trinitroethyl trinitrobutyrate,bis(trinitroethy1) urea,

and trinitroethyl nitrate.

Other polymeric fuels which may be used include any of the knownhydrocarbon polymers, polymers containing nitrogen, such aspolyacrylonitrile, natural rubber (polyisoprene), polyvinyl ethers, andcombinations of two or more such polymers. Pblymeric materialscontaining oxygen in non-plosophoric groups such as hydroxyl, ether,carboxyl, etc. where the oxygen has been partially reduced by beingattached to the carbon atom are suitable fuel binders.

The point in the process at which polymerization of the fuel binder isachieved will depend upon the fuel binder chosen and the degree ofcompatibility existing between the oxidant and various degrees ofpolymerization of the fuel binder. Thus, the fuel binder may becompletely polymerized before adding the high-energy oxidant; it may bepartially polymerized before the oxidant is added and thenpolymerization completed; or the oxidant may be added to theunpolymerized fuel-binder and then polymerization accomplished.

Small quantities of suitable plasticizers or stiffening agents (in theorder of a few percent) may be required to gllVE the propellant suitablehandling properties. Their use depends upon the polymer chosen. Thenecessity for such plasticizers or stiffening agents may be eliminatedby blending two or more of the polymeric fuels to obtain the desiredconsistency for the final propellant. How this may be done isillustrated in Example 1 below. Also, small quantities of stabilizingagents may be added to prevent deterioration in storage. The plasticizermay be inert as diethylhexyl sebacate, or may be a high-energy materialitself such as a polyglycol nitrate. Agents for controlling the burningrate of the propellant may also be added. For example, deterrents suchas dinintrotoluene may be included to decrease burning rates whilecompounds such as described in my co-pending application Serial No.516,374, filed June 20, 1955, now abandoned, may be added to increaseburning rates.

Compounding of the oxidizing agent and fuel may be carried out in asuitable solvent, such as carbon tetrachloride, chloroform, xylene, orother suitable aromatic or aliphatic hydrocarbon solvents including theso-called rubber solvents, to make an easily workable propellant.

One method which I have found preferable is to cool rap-idly a solutionof the oxidant, fuel binder, and other additives such as stabilizers, inthe solvent with vigorous agitation, and then mixing thoroughly in amultiple roll mill.

The compounding of the oxidizing agent and fuel may also be done undersolventless conditions if the polymer serving as the fuel binder is in asuitable physical state for such solventless mixing. This method ofmixing may be used when the fuel binder is added in an unpolymerized orpartially polymerized state.

Propellants thus formulated may be extruded and cut or processed in anymanner indicated by the use the propellant is to be put.

The following examples, which are considered as illustrative rather thanlimiting, Will serve to explain the present invention in more detail.

EXAMPLE I Twenty grams of bis(trinitroethyl)nitramine, 3.5 grams ofpolyethylene, and 22.5 grams of a 1/15 solution of polyisobutylene incarbon tetrachloride containing 1.5 grams of polyisobutylene of amolecular wei ht of ap proximately 100,000 were mixed in a glass flask.The mixture was heated to the point where incipient boiling of thecarbon tetrachloride set in. Almost all of thebis(trinitroethyl)nitramine and polyethylene went into solution. Themixture was then poured into a small three-roll mill, the rolls havingbeen precooled with tap Water to a little above the ambient dew point.Milling was continued until sufficient carbon tetrachloride hadevaporated to make the material extrudable and to reduce the particlesize of the explosive which had recrystallized when cooled. Thismaterial was extruded and cut to proper length in the conventionalmanner for smokeless powder manufacture. The final extruded and cutmaterial was dried by a current of Warm air.

EXAMPLE II High-Impulse RDX Powder Five grams of polyisobutylene havinga molecular weight of about 120,000 was dissolved in a mixture of 50 ml.of a light petroleum solvent boiling range 83- 100 F., and 50 ml.benzene. This three-component mixture was put in a mixer and 45 grams ofcyclotrimethylene-trinitramine (RDX) was added in the form of a veryfine, dry powder (300- mesh or finer). The mixer was run until a uniformmixture was obtained, about to min. RDX is substantially insoluble inthe solvents used but by this method is satisfactorily suspended in thebinder. The soft mass was passed through a three-roll pigment mill untilit became the proper consistency for extrusion. The extrusion, cutting,drying, etc. were conventional. This powder contained 90 RDX and 10%polyisobutylene.

EXAMPLE III Cool RDX Powder Five grams of polyisobutylene having amolecular weight of about 120,000 was dissolved in 50 ml. of a lightpetroleum solvent, boiling range 83-100 F. Three grams of polyethylenewas mixed with 50 ml. of benzene and heated to boiling to causesolution. This solution Was poured into the polyisobutylene solutionwith vigor ous stirring. Much of the polyethylene came out of solutionbut appeared to be in such finely divided form that it mixedsatisfactorily with the other ingredients. This mixture was put in themixer and 42 grams of RDX added in a finely powdered form (300 mesh).The milling, mixing, extruding and processing were the same as inExample II. This powder contained 84% RDX, 10% polyisobutylene and 6%polyethylene.

In deterring these propellants by the simple expedient of depositing athin layer of slow burning material on the outside of the grain thetechnique of dififusion coating is not practical. This is becausecrystal faces of the organic high-energy material are exposed on thesurface of the grains and the deterrent will not difluse into suchcrystal faces. Deterrents may therefore be put on as a separate layer,usually on the outside if it is a grain of one composition only, or asone of the layers in a multilayer grain.

The powders formulated in the manner described in this invention providepropellants for such applications as small arms ammunition which arecapable of producing higher bullet velocities than previously attained,or which require less powder for velocities comparable to those nowachieved. These propellants also provide a, flexibility in performancecharacteristics hitherto not achieved.

I claim:

1. A new-type propellant composition in the form of discrete solidpieces and consisting essentially of an intimate mixture of a solidhigh-energy, organic, oxygencontaining compound the oxygen of which iscontained in a radical selected from the group consisting of nitrate,aromatic nitro, aliphatic nitro, nitramine, nitroso, peroxide, ozonideand perchlorate, the number of atoms of oxygen in said radical beinggreater than the number of atoms of carbon in said high-energy organiccompound, and a hydrocarbon, polymeric fuel binder incapable ofsupporting its own combustion and selected from the group consisting ofpolyethylene, polyisobutylene, polyacrylonitrile, natural rubber,polyvinyl ether, and mixtures thereof; the weight ratio of saidhigh-energy organic compound to said polymeric fuel binder being soadjusted as to provide at least one atom of oxygen for each atom ofcarbon in said high-energy compound and said fuel binder.

2. Propellant in accordance with claim 1 wherein said high-energyorganic compound is cyclotrimethylenetrinitramine.

3. A new-type propellant composition in the form of discrete solidpieces and consisting essentially of an intimate mixture of a solidhigh-energy organic oxygen-containing compound selected from the groupconsisting of bis(trinitroethyl)nitra m i n ecyclotrimethylenetrinitramine, cyclotetramethylenetetranitramine,methylenedinitramine, trinitroethyl trinitrobutylrate,bis(trinitroethyl)- urea, and trinitroethyl nitrate, and a hydrocarbonpolymeric fuel binder incapable of supporting its own combustion andselected from the group consisting of polyethylene, polyisobutylene,polyacrylonitrile, natural rubber, polyvinyl ether, and mixturesthereof; the weight ratio of said high-energy organic compound to saidpolymeric fuel binder being so adjusted as to provide at least one atomof oxygen for each atom of carbon in said highenergy compound and saidfuel binder.

References Cited in the file of this patent UNITED STATES PATENTS1,408,056 Wohl Feb. 28, 1922 2,541,389 Taylor Feb. 13, 1951 2,606,109Kistiakowsky Aug. 5, 1952 2,622,277 Bonell et a1 Dec. 23, 1952 OTHERREFERENCES Military Explosives TM9-1910, T011A-1-34, April 1955, pp.229231.

1. A NEW-TYPE PROPELLANT COMPOSITION IN THE FORM OF DISCRETE SOLIDPIECES AND CONSISTING ESSENTIALLY OF AN INTIMATE MIXTURE OF A SOLIDHIGH-ENERGY, ORGANIC, OXYGENCONTAINING COMPOUND THE OXYGEN OF WHICH ISCONTAINED IN A RADICAL SELECTED FROM THE GROUP CONSISTING OF NITRATE,AROMATIC NITRO, ALIPHATIC NITRO, NITRAMINE, NITROSO, PEROXIDE, OZONIDEAND PERCHLORATE, THE NUMBER OF ATOMS OF OXYGEN IN SAID RADICAL BEINGGREATER THAN THE NUMBER OF ATOMS OF CARBON IN SAID HIGH-ENERGY ORGANICCOMPOUND, AND A HYDROCARBON, POLYMERIC FUEL BINDER INCAPABLE OFSUPPORTING ITS OWN COMBUSTION AND SELECTED FROM THE GROUP CONSISTING OFPOLYETHYLENE, POLYISOBUTYLENE, POLYACRYLONITRILE, NATURAL RUBBER,POLYVINYL ETHER, AND MIXTURES THEREOF; THE WEIGHT RATIO OF SAIDHIGH-ENERGY ORGANIC COMPOUND TO SAID POLYMERIC FUEL BINDER BEING SOADJUSTED AS TO PROVIDE AT LEAST ONE ATOM OF OXYGEN FOR EACH ATOM OFCARBON IN SAID HIGH-ENERGY COMPOUND AND SAID FUEL BINDER.